The present invention relates to a heating device such as an electric heater for removing frost and ice produced in an evaporator of an evaporation apparatus such as an evaporator or the like or in an outdoor heat exchanger of a heat pump.
In the prior art evaporation apparatus such as evaporators, frost produced on an evaporator is defrosted by means of an electric heater, a hot gas or the like in response to the defrosting instruction generated when the operation time of a compressor is integrated to a predetermined time period (for instance 8 hours). As compared with a defrosting system of the type wherein defrosting operations are periodically carried out at a predetermined time interval independently of the operation cycles of the compressor, the defrosting system described above is more efficient because useless defrosting operations are less. However, an operation integration time is set depending upon a maximum amount of frost in the case of high environmental temperatures (humidity) in summer so that in the case of low environmental temperatures (for instance 10.degree. C.) in winter, at a stage at which the operation integration time of the compressor exceeds 8 hours, an actual amount of frost is less so that when the environmental temperature is maintained almost unchanged, there will often be no hindrance even when the defrosting operation is started after 8 hours. In the case of the heat pump, the period of the defrosting operations of an outdoor heat exchanger which is set to a lowest temperature at which the operation of the heat pump is possible is too short at relatively high environmental temperatures. In this period, there will be no hindrance even when the number of defrosting operations is reduced.